1. Technical Field
The present invention relates to a scanning unit of a position measuring arrangement. The scanning unit includes a regulating device for controlling the amplitude of at least one analog scanning signal of the scanning unit and a display unit for signalizing the size of the amplitude.
2. Background Information
The control of the scanning signals is in particular required during mounting of the scanning unit. The signal quality, and therefore the accuracy of measurement, depends to a considerable extent on the exact adjustment of the scanning unit relative to the scale. In order to assure a high degree of accuracy in connection with incremental position-measuring arrangements, the scanning signals generated by the scanning unit should be of large and have equal amplitudes, and have a mutual phase offset of 90° as well. Amplitude is essentially determined by the position of the scanning unit relative to the scale, this means distance, twist and lateral displacement of the scanning unit relative to the scale.
In accordance with EP 0 514 081 B1, the scanning signals are supplied to a regulating device, which compares the amplitude with a threshold limit. If the amplitude lies below this threshold value, a display unit is activated, which is used as an indication that the scanning unit has been incorrectly installed in relation to the scale.
It is disadvantageous here that the display unit only indicates by the illumination of a green or a red light source whether the scanning head has been correctly or incorrectly installed.
It had already been noted that this indication alone is not sufficient for the installation, and that it would be advantageous for the user to also receive an indication regarding the actual size of the amplitude. In connection with this it has now been proposed in DE 101 57 112 A1 to compare the amplitude of the scanning signal with a predetermined desired value and, depending on the size of the deviation, the light luminosity of a light source as the display unit varies.
In this connection, it is disadvantageous that the association of the light luminosity and the amplitude size is difficult for the user.